The objective of the present investigation was to synthesize nitro and bromo derivatives of 4-hydroxycoumarins, 4,7-dihydroxycoumarins and their C-methylated derivatives by ultrasound irradiation and assess the lipophilicity of these coumarin derivatives by shake-flask method with octanol-water as solvent. Log P values were also calculated with HYPERCHEM software. The results indicated that 4,7-dimethylcoumarin and 6-bromo-4,7-dimethylcoumarin possess the highest lipophilicity. The lipophilic value calculated by shake flask method reveals that 4-methyl 7-hydroxy-6-nitrocoumarin, 4-methyl 7, 8-dihydroxy-6-nitrocoumarin and 6-bromo-4,7-dihydroxycoumarin have high lipophilic value.